Wireless, radio or cellular technologies (GERAN, UTRAN, E-UTRAN, WiFi, etc.) require spectrum resources to establish communication. Spectrum is fundamental to the success of mobile wireless communications, and mobile operators often rely on an exclusive license as a key asset ensuring predictable service as well as business fundamentals.
The range of spectrum that is made available for mobile communication has increased over the years, but despite this the demand for new spectrum still exceeds the available exclusive spectrum. The scarcity of spectrum has created a need for new methods to assign spectrum resources and sharing licensed spectrum with other operations.
One framework to address the sharing of spectrum is Licensed Sharing Access (LSA), also sometime referred to as Authorized Shared Access (ASA) or Spectrum Access System (SAS). Within this framework it would be feasible for an operator or other licensee to use spectrum that is partly utilized already by other users/applications. The entity or service operator that operates the application is called incumbent. The incumbent could operate applications like Radar, Fixed Satellite System or the like, but the applications could also include more ad hoc applications like Programme Making and Special Events (PMSE).
The ASA/LSA/SAS schemes define spectrum resource and sharing rules that may be manifested into exclusion/protection zones. The users sharing the spectrum with, for example, the incumbent users need to adhere to those rules. The rules may be changed/updated during the life-time of a sharing agreement. The spectrum resource and sharing rules are typically exchanged over an interface between the relevant parties.
A basic framework to handle sharing of spectrum and interference between applications has been defined in IETF Protocol to Access White-Space Databases (PAWS). The framework of LSA, however, extends beyond the capabilities in IETF PAWS.
Standardization of an LSA framework and related interfaces are ongoing in the ETSI Reconfigurable Radio Systems (RRS) project. In parallel, the Federal Communication Commission (FCC) in the US is defining the regulatory framework for use of 3.5 GHz spectrum as a step in the President's Council of Advisors on Science and Technology (PCAST) recommendations to identify 1000 MHz of federal spectrum to create “the first shared use spectrum superhighways.”
In ETSI, the standard has defined an LSA system comprising a so-called LSA Repository (LR) and a so-called LSA Controller (LC). The LSA Repository hosts the functions to input, store and process data from a regulator and one or more incumbents. After processing the available spectrum resources and the restrictions set up by regulator and incumbent, the LSA Repository will communicate the restrictions to the LSA Controller either as part of an Availability Request procedure (LSA Controller Request information, pull procedure) or Availability Notification procedure (LSA Repository pushes information to the LSA Controller)
The exchange of information is required for the LSA Controller to manage the cell configuration within a cellular network, i.e., either activate or de-activate a cell, modify cell parameters, e.g., output power, or other changes required in the cellular network to comply with regulations and incumbent protection requirements.
The communication between LSA Repository and LSA Controller over an interface, LSA1 assumes a persistent connection that allows for continuous communications to ensure that the LSA Controller has up-to-date information. For verification that the interface is up and running, different techniques can be used (e.g., heartbeat or similar techniques). However, there is no means available to ensure that the communication over LSA1 will never fail. And the higher the availability requirements, the more the cost increases.
In this case the only default fallback that ensures compliance to the regulatory and incumbent restrictions is to de-activate the cells that are sharing spectrum since it is not possible to know if the LSA Controller is up-to-date. This approach would potentially impact the service provided by an operator, resulting in service degradation since it may need to stop using these frequencies.